Betulinic acid chemosensitizes breast cancer by triggering ER stress-mediated apoptosis by directly targeting GRP78

Abstract

Stress-induced cellular defense machinery has a critical role in mediating cancer drug resistance, and targeting stress-related signaling has become a novel strategy to improve chemosensitivity. Betulinic acid (BA) is a naturally occurring pentacyclic triterpenoid with potent anticancer bioactivities in multiple malignancies, whereas its underlying mechanisms remain unclear. Here in, we found that BA has synergistic effects with taxol to induce breast cancer cells G2/M checkpoint arrest and apoptosis induction, but had little cytotoxicity effects on normal mammary epithelial cells. Drug affinity responsive target stability (DARTS) strategy further identified glucose-regulated protein 78 (GRP78) as the direct interacting target of BA. BA administration significantly elevated GRP78-mediated endoplasmic reticulum (ER) stress and resulted in the activation of protein kinase R-like ER kinase (PERK)/eukaryotic initiation factor 2a/CCAAT/enhancer-binding protein homologous protein apoptotic pathway. GRP78 silencing or ER stress inhibitor salubrinal administration was revealed to abolish the anticancer effects of BA, indicating the critical role of GRP78 in mediating the bioactivity of BA. Molecular docking and coimmunoprecipitation assay further demonstrated that BA might competitively bind with ATPase domain of GRP78 to interrupt its interaction with ER stress sensor PERK, thereby initiating the downstream apoptosis cascade. In vivo breast cancer xenografts finally validated the chemosensitizing effects of BA and its biofunction in activating GRP78 to trigger ER stress-mediated apoptosis. Taken together, our study not only uncovers GRP78 as a novel target underlying the chemosensitizing effects of BA, but also highlights GRP78-based targeting strategy as a promising approach to improve breast cancer prognosis.

XIAOPI formula inhibits the pre-metastatic niche formation in breast cancer via suppressing TAMs/CXCL1 signaling

“…Tumor specimens were fixed in 4% paraformaldehyde for 24 h, followed by the protocol as we described previously [17]. Hematoxylin and Eosin staining was conducted using the Hematoxylin and Eosin Staining Kit (Beyotime Biotechnology, Shanghai, China) according to the manufacturer's instructions.…”

Betulinic Acid Attenuates T-2-Toxin-Induced Testis Oxidative Damage Through Regulation of the JAK2/STAT3 Signaling Pathway in Mice

“…The results of this work showed that BA supplementation reversed the ratios of p-JAK2/JAK2, p-STAT3/STAT3, and Bax/Bcl-2, and reduced the activation of caspase-3, which was confirmed by the TUNEL results; these data suggest that T-2-toxin-induced apoptosis was blocked by BA treatment. Accumulating evidence has demonstrated that BA is able to induce apoptosis in a broad variety of cell types, including human cervical cancer cells, breast cancer cells, and HT-29 colorectal cancer cells [41][42][43]. In our experiment, BA acted as an antiapoptotic agent in the testes of mice treated with T-2 toxin.…”

Psoralen inhibits malignant proliferation and induces apoptosis through triggering endoplasmic reticulum stress in human SMMC7721 hepatoma cells

“…Once ER-stress, a large number of unfolded or misfolded proteins will snatch GRP78 that originally binds to three kinds of responsive proteins, making them exposed and activated. At present, it has been found that GRP78 is closely related to the occurrence and development of liver cancer [43], breast cancer [44] and lung cancer [45]. The expression of GRP78 is increased when ER-stress occurs, which can promote the misfolded or unfolded protein to normal status, thereby reducing the endoplasmic reticulum load and maintaining the stability of the intracellular environment.…”